A) Field of the Invention
The present invention relates to a semiconductor light emitting device and its manufacture method.
B) Description of the Related Art
With reference to FIG. 22, description will be made on a light emitting device disclosed in U.S. Pat. No. 6,885,034. A semiconductor layer 1028 is formed on a substrate 1014, with a low resistance semiconductor layer 1018 being interposed therebetween. An electrode is connected to the semiconductor layer 1018. A reflection layer 1015 is formed on the bottom surface of the substrate 1014. An optical emission layer 1026 is formed on the semiconductor layer 1028, and a semiconductor layer 1027 is formed on the optical emission layer 1026. The semiconductor layers 1028 and 1027 have opposite conductivity types.
Dents 1030 are formed through the semiconductor layer 1027 and optical emission layer 1026 to expose the semiconductor layer 1028 on the bottom of the dents 1030. A translucent electrode layer 1024 of NiO/Au is formed covering the upper surface of the semiconductor layer 1027. The translucent electrode layer 1024 is not formed on the inner surfaces of the dents 1030.
After the translucent electrode layer 1024 is formed on the semiconductor layer 1027, the translucent electrode layer 1024, semiconductor layer 1027, optical emission layer 1026 and semiconductor layer 1028 are removed by reactive ion etching to form the dents 1030.
Light radiated from the optical emission layer 1026 propagates through the translucent electrode layer 1024 or through the insides of the dents 1030 and is outputted to the space above the light emitting device. Light passing through the translucent electrode layer 1024 is partially absorbed therein. Light output from the insides of the dents 1030 is not absorbed in the translucent electrode layer 1024. Therefore, the dents 1030 increase the amount of light to be output from the light emitting device.
Next, with reference to FIGS. 20A and 20B, description will be made on a light emitting device having a lattice electrode. FIG. 20A is a schematic plan view of the light emitting device.
This light emitting device has an n-type nitride semiconductor layer 102, an optical emission layer 103 formed on the n-type nitride semiconductor layer 102, and a p-type nitride semiconductor layer 104 formed on the optical emission layer 103. An optical emission region 950 is defined on the surface of the p-type nitride semiconductor layer 104, the optical emission region 950 having a square shape with a recessed central area along one side thereof. The p-type nitride semiconductor layer 104 and optical emission layer 103 and a surface layer of the n-type nitride semiconductor layer 102 are removed from an area surrounding the optical emission region 950, to thereby form a recess 911 exposing the n-type nitride semiconductor layer 102 on the bottom of the recess.
A p-side electrode 905 is formed on the optical emission area 950. The p-side electrode 905 is constituted of a lattice portion 905a and a p-side pad portion 905b. The lattice portion 905a has a lattice structure. The p-side pad portion 905b is formed in a central area of the side opposing the recessed side, covering the lattice portion 905a. An n-side electrode 907 is formed on the bottom of the recess 911. The n-side electrode 907 is disposed in a recessed area of the optical emission region 950. The n-side electrode 907 is used as a pad.
As a predetermined voltage is applied across the p-side electrode 905 and n-side electrode 907, light is emitted from the optical emission layer 103. The material used for the p-side electrode 905 may not be transparent to light emitted from the optical emission layer 103. Light can be output to an exterior of the light emitting device from the upper surface of the device where the p-side electrode 905 is not formed.
In the light emitting device of U.S. Pat. No. 6,885,034, the upper surface of the semiconductor layer 1027 where the dents 1030 are not formed, is covered with the translucent electrode layer 1024. Light to be passed through the translucent electrode layer 1024 and to be output to the exterior is attenuated by absorption in the translucent electrode layer 1024. It is therefore difficult to improve an optical output efficiency.
In the light emitting device described with reference to FIG. 20A, a strong electric field is likely to be generated near the n-side electrode 907, and current is likely to flow at a high current density. As current flows at a high current density, the optical emission layer is likely to be degraded.